Heat treatment of manganese steel



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Ho mrawlng. Application filed September of Illinois, have invented certain new and useful Improvements in Heat Treatment of Manganese Steel, of which the following is ga ecification.

j y invention relates to the heat treatment of manganese steel.

v The most important step in the manu-.

facture of manganese steel is the heat treatment thereof. This is especlally true as to castings, as manganese castlngs are worthless. as coercial products, unless properly heat treated. The structure of manganese steel in the cast state is austenitic, but around the grain boundaries is found a heavy separation of carbide which causes brittleness, theobject of the heat treatment being to dissolve this carbide, and the application of heat is continued until all of t e carbide is dissolved.

There-are two methods generally used at .725 the present time for heat treating manganese steel castin s. One is the employment of a coal fired mace, and the other an oil or gas firedfurnace. In each of thesefurnaces the same fundamental arrangement prevails, in the case. of coal. a grate extends usually the entire depth of the furnace and has several firing doors. Between the grate and the portion of the furnace in which the castings are placed is constructed a bridge 'or fire Wall, for the purposeof preventing the flame from playingdirectly on the casting. In the oil or burners are substituted in place of grates and are directed so that the flames of com to bustion play against the bridge wall similar to the coal fired furnaces. A great'objection to such types of aces is that the side of the chamber opposite the wall will heat much more quickly than that portion directly behind the bridge 'wall. Furthermore, the castings on. the top of the pile are heated more quickly than the castings nearer the bottom. This uneven heating 1s one of the main causes for cracked cast- 5o ings. Where coal is used, proper operation of the furnace depends on the ability of the man doing the firing. Often times the fire at one end of the grate is hotter than at the other, which means that one part gas fired furnace,

Specification of Letters Patent. Patemfgqgd Aug, 2%) ggg re, nae. sexier no. 411,250.

temperature ahead of another part, and in the case of velg large castings, undue strains are set up. ecause of this uneven heat- -i ng,'cracks develop and the castings are reected. With oil fired furnaces, trouble is quality of oil. Another objection to any type where the successful operation of the furnace depends on theoperator is that the furnace-tender may crowd his furnace too much, especially is this true'in bringing the castings from atmosphereic temperature to red heat. Many castings have been rejected because the furnace operator has crowded his furnace too much during the early stages of heat treatment. Another objection to the coal and oil and gas fired furnaces is that because of the smoke in the furnace, it is impossible for the operator to judge the temperature correctly. This is especially-true during the latter portion of the heat treatment, as the castings may be within a few degrees of the correct temperature and the operator applies more fuel to raise the temperature these few degrees and very often overheats the castings.

. A further objection to the present type of furnace is that of oxidization, as oxygen is essential to proper combustion of coal, gas, or oil, and in certain classes of castings, the outer surfaces thereof are oxidized to such an extent as to permit exceedingly great wear after being placed in service. This feature is especially noticeable in railroad Work such as crossings and fi'ogs.

Another objection to the present method of heat treatment is the tendency to overheat the thin sections in order to thoroughly heat the thick sections. This is especially true where larger castings are undergoing treatment, or Where castings are of uneven to experienced because of the variation in the sections. In the present practice, these sec-r Add 55 of the furnace will be heated to properhmanganese castings in an elcctric furnace no v of the resistance type and heating the fun nace. a The amount of heat delivered to the furnace is at all times no higher than that 'necessary to dissolve the-carbon about the grain boundaries. 1 have-found that it is possible to put thin, thick, large, and small castings in the same furnace, and have treated these successfully, securing complete dissolution of the carbide without harming any of the castings. When the castings are put in the furnace, the same is hot from the previous heat treatment, let'it be assumed about;

MOW F. As soon as the lot is put in the furnace, the temperature thereof will drop quickly,- due to the heat absorption by the castings. The smaller castings and the'thin sections tend to come to the temperature-of the furnace faster than the thick sections,

but beforea critical temperature'is reached, the. entire furnace temperature would be very low, so that no harm is done to any of the castings. Then the furnace temperature would rise slowly, bringing the temerature of the casting with it, the light and heavy sections absorbing the increased heat. In practicin my invention, 1 provide suit.- able means or cutting oh the electric current as soon as the desired 'temperathre within the furnace is obtained. In this manner no damage whatsoever can be caused to the'castings. By my invention it is possible also to eliminate constant attention by an attendant, make a cleaner shop, and better working conditions. With my invention it is possible, as before stated, to put small, large, thin, and thick castings into a single furance without any fear of damage to thesame, Whereas in the coal,

gas, or oil fired furnaces, it is necessary to separate the castings so as to put those of substantially thesame thickness of sectionin a single furnace. This is possible in my invention by reason of the fact that the- Mamet small casting can not-absorb more heat than treating manganese steel castings, which.

consists in subjecting such castings to heat,

the'maximum temperature of which never exceeds the criti castings. 2. An

a1 temperature for such consists in heating the same in a non oxidizing atmosphere by maintaining the temperaimprovement-dn the art of heat. treating manganese steel 'castingswhich ture below .the critical temperature of said castings.

i 3. An v treating manganese steel castings which improvement in the art of heat consists in subjecting the same toheat in a v non-oxidizing atmosphere in which the heat is -maintained below the critical temperature for such castingsbut up to a degree suficient to dissolve the carbides-in the steel.

4. An improvement in the art of heat treating manganese steel castings which consists in subjecting the same to the heat of-an electric furnace, in which the maximum temperature never exceeds the critical temperature for. such castings.

5. An improvement in the art of heat treating manganese steel castings which consists inheating the same in an electric resistance furnace and maintaining the same below the critical temperature of said castings. v

,Signed at Chicago, Cook 00., 111., this eleventh day of September, 1920.

WESLEY Gr. NICHOLS. 

